Please read the kvm-quickstart instructions first, since this will allow you to get started quickly.
If you don't have any familiarity with xfstests, you may also want to read this introduction to xfstests.
The kvm-xfstests system consists of a series of shell scripts, and a test appliance virtual machine image. You can build an image using the build infrastructure in the xfstests-bld git repository, but if you are just getting started, it will be much simpler if you let kvm-xfstests automatically download a pre-compiled VM test appliance image from kernel.org.
There are prebuilt test appliances for 32-bit and 64-bit x86 systems (root_fs.img.i386 and root_fs.img.amd64) as well as for the 64-bit ARM platform. Thet test appliance images are installed in the test-appliance directory, but it's easist to just allow kvm-xfstests to download the image to the correct place, or to let the build-appliance write the newly created test appliance image where it should be located. If you want to build your own test appliance VM, see building-rootfs.md.
The configuration file for kvm-xfstests is located ~/.config/kvm-xfstests. A sample of the parameters that can be set in the config file can be found in run-tests/config.kvm and run-tests/config.common, which show the default values if they are not overridden by settings in ~/.config/kvm-xfstests.
Perhaps the most important configuration variable to set is KERNEL. This should point at the default location for the kernel that qemu will boot to run the test appliance. This is, in general, should be the primary build tree that you use for kernel development. If kvm-xfstests is run from the top-level of a kernel build or source tree where there is a built kernel, kvm-xfstests will use it. Otherwise, it will use the kernel specified by the KERNEL variable.
To build a correctly configured kernel for use with kvm-xfstests, run the commands:
install-kconfig
kbuild
If you wish to build kernels for the i386 or arm64 platforms, add "--arch i386" or "--arch amd64" to install-kconfig and kbuild commands.
By default, the scratch disks used by test-appliance will be set up automatically, and are stored in the run-fstests directory with the names vdb, vdc, vdd, ... up to vdg. However, it is slightly faster to use logical volumes. To do this override the VDB..VDG variables in the ~/.config/kvm-xfstests file.
VG=closure
VDB=/dev/$VG/test-4k
VDC=/dev/$VG/scratch
VDD=/dev/$VG/test-1k
VDE=/dev/$VG/scratch2
VDF=/dev/$VG/scratch3
VDG=/dev/$VG/results
If you chose to do this, the logical volumes for VDB, VDC, VDD, and VDG should be 5 gigabytes, while VDE and VDF should be 20 gigabyte logical volumes. The devices VDB and VDG should have an ext4 file system created using the mkfs.ext4 command before you try running kvm-xfstests.
The kvm-xfstests shell script is in the run-fstests directory, and it is designed to be run with the current working directory to be in the run-fstests directory. For convenience's sake, the Makefile in the top-level directory of xfstests-bld will create a kvm-xfstests shell script which can be copied into a convenient directory in your PATH. This shell script will set the KVM_XFSTESTS_DIR environment variable so the auxiliary files can be found and then runs the run-fstests/kvm-xfstests shell script.
Please run "kvm-xfstests help" to get a quick summary of the available command-line syntax. Not all of the available command-line options are documented; some of the more specialized options will require that you Read The Fine Source --- in particular, in the auxiliary script file found in run-fstests/util/parse_cli.
The general form of the kvm-xfstests command to run tests in the test appliance is:
kvm-xfstests [-c <cfg>] [-g <group>]|[<tests>] ...
By default defaults to all, which for ext4 will run the following configurations: "4k", "1k", "ext3", "encrypt", "nojournal", "ext3conv", "adv", "dioread_nolock, "data_journal", "inline", "bigalloc_4k", "bigalloc_1k", and "dax". You may specify a single configuration or a comma separated list if you want to run a subset of all possible file system configurations.
Tests can be specified using an xfstests group via "-g ", or via one or more specific xfstests subtests (e.g., "generic/068"). The most common test groups you will use are "auto" which runs all of the tests that are suitable for use in an automated test run, and "quick" which runs a subset of the tests designed for a fast smoke test.
For developer convenience, "kvm-xfstests smoke" is short-hand for "kvm-xfstests -c default -g smoketest --soak-duration 3m". In addition "kvm-xfstests full" is short-hand for "kvm-xfstests -g auto" which runs all of the tests using a large set of file system configurations. This will take the better part of a day, so you should consider running the full set of tests using "gce-xfstests ltm full", which will start multiple VM's for each file system configuration, and will take a few hours, if you have access to a GCE account.
The command "kvm-xfstests shell" will allow you to examine the tests environment or to run tests manually, by booting the test kernel and requesting that the test appliance VM start an interactive shell.
Any changes to the root partition will be reverted when you exit the VM. If you would like to modify the root_fs.img appliance permanently, you can run "kvm-xfstests maint" instead.
You can run tests manually by looking at the environment variables set in the /root/test-env file (which is sourced automatically when you start an interactive shell). You can then set FSTESTCFG and FSTESTSET to control which tests you would like to run, and then run the test runner script, /root/runtests.sh. For example:
% kvm-xfstests shell
# FSTESTCFG="4k encrypt"
# FSTESTSET="generic/001 generic/002 ext4/001"
# /root/runtests.sh
...
To stop the VM, you can run the "poweroff" command, but a much faster way to shut down the VM is to use the command sequence "C-a x" (that is, Control-a followed by the character 'x').
While kvm-xfstests is running, you can telnet to a number of TCP ports (which are bound to localhost). Ports 7500, 7501, and 7502 will connect you to a shell prompts while the tests are running (if you want to check on /proc/slabinfo, enable tracing, etc.) You can also use these ports in conjunction with "kvm-xfstests shell" if you want additional windows to capture traces using ftrace.
You can also access the qemu monitor on port 7498, and you can debug the kernel using remote gdb on localhost port 7499. Just run "gdb /path/to/vmlinux", and then use the command "target remote localhost:7499".
Pro tips for using remote gdb: it's helpful to temporarily add "EXTRA_CFLAGS += -O0" to fs/{ext4,jbd2}/Makefile, and use a kernel config with debug features enabled via "kvm-xfstests install-kconfig --debug". In addition, you may need to add to your $HOME/.gdbinit the line "add-auto-load-safe-path /path/to", where /path/to is the directory containing the compiled vmlinux executable. See Documentation/dev-tools/gdb-kernel-debugging.rst in the kernel sources for more information.
By default, when test results are saved in the run-fstests directory with the filename log..
The get-results command will summarize the output from the log file. It takes as an argument the name of the log file; if no log file is specified, then the get-results command will display a summary of the most recent log file.